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The present invention relates generally to mechanical rate gyroscopes, and more specifically to mechanical rate gyroscopes having transduction coefficients that are less sensitive to the mechanical and electrical properties of the gyroscopes.
Mechanical rate gyroscopes are known that employ the Coriolis effect to provide a measure of an applied angular rate. In a conventional mechanical rate gyroscope, a body with a mass, m, is supported by a flexible suspension system from a rigid accelerometer frame. The body is caused to vibrate at a velocity, v, by a drive force, Fd, as the rigid frame rotates at an applied angular rate, xcexa9IN, about a rate-sensing axis perpendicular to the velocity of the body. The combined vibration and angular displacement causes the body to undergo Coriolis acceleration, Ac=2vxcexa9IN, in a direction perpendicular to both the velocity and the rate-sensing axis. Accordingly, a Coriolis force, Fc=mAc, is applied to the body, thereby causing the body to deflect in the direction of the Coriolis acceleration.
In the conventional mechanical rate gyroscope, such deflection of the body is typically restrained by either a mechanical or electrical restraint, e.g., a mechanical spring having a spring constant, k. The deflection of the body in the direction of the Coriolis acceleration may therefore be defined by the expression, y=Fc/k. Moreover, the deflection of the body is typically measured using a displacement sensor such as a device that measures a difference in capacitance caused by a change in the spacing between parallel plates of a capacitor. If one plate of the capacitor is operatively coupled to the body and the other plate is fixed to the rigid frame, then the change in the spacing between the plates is proportional to the deflection of the body. Such a displacement sensor produces an output that is proportional to the applied angular rate, xcexa9IN; and, the proportionality constant, K, is commonly known as the sensitivity of the rate gyroscope.
The sensitivity, K, of the conventional mechanical rate gyroscope typically includes a plurality of transduction coefficients, which are functions of the mechanical dimensions, material properties, and electronic gains of the gyroscope and its supporting circuitry, and the voltages, currents, and fields applied thereto. The output of the conventional mechanical rate gyroscope is therefore subject to the various uncertainties and instabilities of these transduction coefficients. Such uncertainties and instabilities are typically minimized by measuring and trimming the transduction coefficients during the manufacturing process, and/or by providing specialized signal conditioning circuitry at the gyroscope output. However, such added manufacturing steps and signal conditioning circuitry can significantly increase the size and cost of mechanical rate gyroscopes, particularly, micro-fabricated mechanical rate gyroscopes.
It would therefore be desirable to have an improved mechanical rate gyroscope with transduction coefficients that are less sensitive to the mechanical and electrical properties of the gyroscope. Such an improved mechanical rate gyroscope would have a reduced size and would be fabricated using a simplified manufacturing process, thereby reducing the overall cost of the gyroscope. It would also be desirable to have such an improved mechanical rate gyroscope that can be fabricated using conventional silicon micro-machining techniques.
In accordance with the present invention, a mechanical rate gyroscope is provided which has transduction coefficients that are less sensitive to the mechanical and electrical properties of the gyroscope. The mechanical rate gyroscope includes a first segmented drive system used to impart vibration to a mass, and a transverse segmented drive system formed from similar segments and used to generate a feedback force to cancel a Coriolis force applied to the mass when the gyroscope undergoes angular displacement. The mechanical rate gyroscope further includes a force-feedback control mechanism used to provide at least one complete cycle of the drive signal employed by the first drive system to the transverse drive system. The force-feedback control mechanism generates a feedback signal used to control the polarity of the complete cycles of the drive signal provided to the transverse drive system. The feedback signal comprises a pulse repetition frequency proportional to the applied angular rate. The proportionality constant relating the applied angular rate to the pulse repetition frequency includes transduction coefficients that are less sensitive to the mechanical and electrical properties of the gyroscope.
Other features, functions, and aspects of the mechanical rate gyroscope will be evident from the Detailed Description of the Invention that follows.